One of the main tests for determining the production capability of a hydrocarbon well exists in stopping production by means of a valve and in recording the changes in pressure due to the well being closed. It is advantageous to be able to close the tubing in the immediate proximity of the underground productive zone in order to eliminate various interfering effects which appear when the closure is performed at the surface because of the compressibility of the fluid present in the tubing.
Preferred embodiments of the present invention provide a closure tool capable of being installed in the tubing of a well while tests are performed on the well, with the valve of said tool being..easy to operate in spite of the considerable pressure which may exist in the well and which opposes re-opening the valve once it has been closed.